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TPS2543: Current Limiting and Mode selection

Tim Riese
Prodigy 100 points
Part Number: TPS2543

Hello,

i wanted to know how the IC regulates the current when a device tries to use more current than the previosly set limit. 
The datasheet mentions that the IC regulates the Voltage down accordingly but not how. 

Furthermore i planned on using the IC to charge a device without a Host on the other end of the data lines. 
Is it still possible to put the device into the mode where it is only allowed to drain 500mA of current using the Datalines?

Thank you for the Help

best regards,
Tim

  • 0
    TI__Mastermind 28830 points

    Hello Tim,

    Question 1

    During an overcurrent condition, the output voltage is reduced by increasing the voltage drop across the power switch. Its outlined in these two sections of the data sheet.

    Question 2

    Yes this is still possible. Just do not connect anything to the DM_OUT and DP_OUT pins, and configure the chip to be in SDP mode as defined in the truth table within the datasheet. This will limit the current limit to 500mA as that is the most an SDP charger can output following the BC1.2 specification.

    Let me know if this answers your questions or not! If so, please click This resolved my issue

  • 0 in reply to Adam Mc Gaffin
    Prodigy 100 points
    Hello Adam,
    thank you for the detailed answer. Question 2 should be solved with this answer.

    One more small Question to clearify regarding topic one. The power switch is in series between IN and OUT, right after the current sense?
    And due to its Voltage regulating feature, the connected device lowers its current to match with the new supplied Voltage?
    Under these circumstances isnt it possible that the Voltage and Current oscillates because the connected device stops charging
    so the IC rises the Voltage and the loop starts over? i had this issue with appledevices and a small resistor to simulate a Voltage drop.

    Regards,
    Tim
  • 0 in reply to Tim Riese
    TI__Mastermind 28830 points

    Hello Tim,

    No, I don't believe this will be an issue. The connected device doesn't lower its current, the TPS2543 just regulates the current to a smaller amount. There should be no voltage drop in a normal current regulated condition.

    However, if there is a short of some kind, then the device uses its over current protection features. Below is a scope shot of a another device that uses the same over current protection. Initially, there is a large current spike. The device recognizes this, and regulates the voltage down, helping to limit the current. From here, an internal timer is enabled and after X amount of time, VBUS is disabled.

    Let me know if this helps answer your question or not!

  • 0 in reply to Adam Mc Gaffin
    Prodigy 100 points

    Hello Adam, 

    im afraid your answer threw up new questions. Maybe a little more detailed description of my plans and Current Sources is helpful.
    I planned to charge up to seven devices over a 5V 5A buck converter and wanted to use the current regulator IC to distribute the current between those devices and shut off those which dont need any charge. 

    The current limit will be set to 500ma for each device. How does the IC react when a device draws more than 500ma? 
    Does it shut down after a certain period of time like you mentioned above?

    Regards,

    Tim Riese

  • 0 in reply to Tim Riese
    TI__Mastermind 28830 points
    Hi Tim,

    If you put the TPS2543 in SDP mode, the portable device will never pull more than 500mA of current. The portable device knows it is connected to an SDP charger, and knows that it can only charge at a max current of 500mA. So the scenario I mentioned above will not occur.